Conventionally, drip irrigation devices have been used to supply irrigation liquids such as water or liquid fertilizer to the plants grown on the soil in the agricultural land, plantation and the like. Regulation of the supply speed of the irrigation liquid with the drip irrigation device enables the saving of the irrigation liquid as well as the management of the growth of the plants.
Such a drip irrigation device includes a drip irrigation dripper. The drip irrigation dripper controls the ejection amount of the irrigation liquid per unit time when ejecting the irrigation liquid having flowed into a flow tube from the water source side (pump side) toward the plants.
One known example of such a drip irrigation dripper is what is called an on-line dripper (see, e.g., PTLS 1 and 2).
On-line drippers are used while being inserted into holes bored in a tube wall (side wall) of polyethylene pipe or into the opening of the end portion of a microtube. On-line drippers are suitable not only for soil culture but also for nutriculture or pot culture when used for greenhouse culture, raising seedling, fruit growing, and the like.
Some on-line drippers have what is called a differential pressure control mechanism (pressure correction function). The drip irrigation dripper is composed of the following three members: an elastic film (e.g., silicone rubber film) such as a diaphragm; an inlet side member and; an outlet side member, as with drip irrigation drippers (emitters) disclosed for example in PTLS 1 and 2. The drip irrigation drippers disclosed in PTLS 1 and 2 have a structure in which the film is sandwiched by the inlet side member and the outlet side member.
The drip irrigation drippers disclosed in PTLS 1 and 2 utilize the operation of the diaphragm (film) in accordance with the liquid pressure of the irrigation liquid having flowed from the inlet to regulate the flow of the irrigation liquid toward a pressure reduction channel on the downstream side of the inlet under low liquid pressure and to control the amount of the outflow of the irrigation liquid from the outlet under high liquid pressure.
More specifically, in the drip irrigation drippers disclosed in PTLS 1 and 2, for example, when the liquid pressure of the irrigation liquid toward the inlet is increased, the diaphragm disposed to block the pressure reduction channel is deflected by the liquid pressure toward the outlet, thereby opening the reduction pressure channel to allow the irrigation liquid to flow into the pressure reduction channel. The irrigation liquid thus having flowed into the pressure reduction channel flows toward the outlet while the pressure of the irrigation liquid is reduced in the pressure reduction channel, and then flows out of the drip irrigation dripper from the outlet. When the liquid pressure toward the inlet is further increased, the amount of the deflection of the diaphragm toward the outlet becomes larger. In association with the larger amount of the deflection of the diaphragm, the sectional size of the channel at the outlet is decreased, and thus the outflow of the irrigation liquid is controlled.